172 CARBON METABOLISM III 



(44) and is also formed by many fungi during the oxidation of quinic 

 acid (53, 57). 



Isotope studies on Neurospora crassa indicate that, as in bacteria, 

 3- and 4-carbon fragments derived from glucose — presumably via the 

 phosphogluconate oxidation pathway (Chapter 7) — combine to form 

 shikimic acid (506). 



As discussed later, currently available information at least encour- 

 ages the speculation that all aromatic compounds arise analogously 

 to protocatechuic acid in N. crassa, i.e., that the normal pathway to 

 aromatic amino acids is blocked or saturated and that the carbon of 

 shikimic acid or its precursors is diverted to the synthesis of new aro- 

 matic structures. However, in N. crassa protocatechuic acid is oxi- 

 dized with ring fission and does not give rise to other aromatic com- 

 pounds. 



Another possibility has been considered by Ehrensvard (176), 

 that pyrones might be intermediates in the conversion of glucose to 

 aromatic compounds by Penicillium urticae. Evidence so far is 

 limited to the action of pyranes, e.g., dehydracetic acid, on the syn- 

 thesis of aromatic compounds. 



Close structural relations among the aromatic compounds are 

 numerous, both within and between species. Many are discussed by 

 Raistrick (430); a few examples may be cited: 



1. Simultaneous formation by one organism of a phenol and the 

 corresponding quinone (14, 180). 



2. Occurrence in the same organism of a compound and its dihydro 

 derivative, e.g., cyclopolic and cyclopaldic acids (Table 4). 



3. Formation of a compound and a hydroxy or methoxy derivative 

 of it, e.g., gladiolic and cyclopaldic acids (Table 4) and methyl cin- 

 namate and methyl-p-methoxycinnamate (74). The ability of fungi 

 to introduce hydroxyl groups into a ring has been noted above in 

 connection with steroid metabolism. 



4. The close structural relationship, already mentioned, of all of 

 the fungal anthraquinones, found in such diverse genera as Aspergil- 

 lus, Cortinarius, Helminthosporium, and Penicillium (289). A pos- 

 sible origin of the anthraquinones from benzophenone is discussed by 

 Tatum (505). 



The foregoing examples refer to more or less static relations. In 

 a dynamic and more conclusive experiment it has been shown that 

 the ratio of patulin to gentisyl alcohol is controlled by the concen- 

 tration of iron in the medium (Figure 7). Similarly, Penicillium 

 urticae in a low-zinc medium forms predominantly 6-methylsalicylic 



